The present invention relates to portable power planers and in particular to an improved cutting blade assembly for a power planer. In general, portable power planers comprise a motor driven rotary cutter head having one or more removable cutting blade assemblies disposed thereon which are adapted to engage and perform a cutting operation upon the surface of a workpiece as the cutter head rotates. The cutting blade assemblies for such tools are adapted to be installed on the cutter head by inserting them into recesses located circumferentially about the cutter head. In one form, the cutting blade assemblies are secured to the cutter head by directly clamping the cutting assemblies to the cutter head with a plurality of threaded fasteners. In another form, complementary shaped recesses are formed in the cutter head and the cutting blade assemblies secured therein by retracting a plurality of bolts from the blade assembly until they contact the opposite surface of the recess and thereby exert a clamping force on the blade assembly.
Blade assemblies as described above generally fall into two categories: a two-piece assembly, comprised of a relatively large cutting blade fastened to a pressure piece or backing, and a three-piece assembly, comprised of a pressure piece, a blade carrier, and a relatively small cutting blade. The pressure piece and blade carrier of the three-piece assembly comprise distinct pieces which are typically loosely fastened or fitted together. For example, one known prior art design utilizes a pressure piece having several projections along its mating surface which are designed to be received within complementary shaped recesses in the mating surface of the blade carrier to enable the pieces to be properly located with respect to each other. The mating surfaces of these two pieces define a slot in which the cutting blade is received.
The known types of cutting blade assemblies described above possess certain advantages and disadvantages. Assemblies of the two-piece type possess the advantage of having a cutting blade which is positively fixed relative to the pressure piece. This feature enables a fixed blade elevation and greatly reduces the possibility of blade ejection if the fasteners retaining the assembly to the cutter head happen to loosen during operation. On the other hand, the two-piece blade assembly possesses the disadvantage of requiring a relatively large and hence costly cutting blade in order to provide a sufficient working surface to enable the blade to be fastened to the pressure piece. Moreover, the changing of cutting blades with such assemblies can be tedious and somewhat time consuming.
The three-piece blade assemblies of the type described above eliminate the need of a separate blade fastener and require a much smaller cutting blade, resulting in an attendant cost savings. However, such assemblies also possess certain disadvantages. In particular, if the clamping bolts of these assemblies should loosen during operation of the tool, it is possible for the pressure piece and the blade carrier to pivot relative to each other, thereby permitting movement of the cutting blade. In other words, since the known types of three-piece cutting blade assemblies all rely exclusively on the clamping force that is exerted between the pressure piece and the blade carrier to secure the cutting blade, it is possible for the blade to be ejected during operation if the clamping bolts should loosen. Moreover, this situation can become aggravated by the wedging and accumulation of wood chips between the blade and the pressure piece. In addition, as none of the pieces of such three-piece assemblies is positively fixed relative to the rest of the assembly prior to the imposition of a clamping force to the assembly, it is sometimes necessary to go through an inconvenient and often tedious procedure of aligning and realigning the mating surfaces of the pressure piece and blade carrier in order to adequately define a proper blade receiving entity and nesting slot when reversing or replacing cutting blades, or otherwise servicing the assembly.
It is therefore an object of the present invention to provide a three-piece cutting blade assembly for installation in a rotary cutter head of a power planer which is adapted to be completely assembled into a single unit prior to insertion in a rotary cutter head.
In addition, it is another object of the present invention to provide a three-piece cutting blade assembly wherein the blade carrier and pressure piece are tightly secured together so as to positively retain the blade therebetween even absent the clamping force exerted on the assembly when installed in the cutter head to thereby preclude the possibility of blade ejection during operation of the tool.
It is a further object of the present invention to provide such an assembly wherein the cutting blade is relatively small and is positively fixed within the assembly without the need for a separate fastener.
Also, it is an object of the present invention to provide such an assembly which enables the assembly to be easily serviced, as well as the cutting blades to be simply and efficiently reversed and replaced.
Briefly, the cutting blade assembly according to the present invention includes an elongated pressure piece having a dove-tail projection extending longitudinally along a face thereof, and an elongated blade carrier which defines a longitudinally extending recess having a plurality of constrictions at spaced locations therealong which enable the recess to tightly receive the dove-tail projection of the pressure piece. These features enable the pressure piece and the blade carrier to be force fitted together with the blade carrier fixed relative to the pressure piece so that the two pieces constitute a single entity. As so assembled, these two pieces define a longitudinally extending blade receiving slot into which the cutting blade of the assembly is laterally inserted. This slot includes a longitudinally extending projection which is adapted to be received within a groove extending along one face of the cutting blade. This blade groove defines a contact surface which engages the slot projection to enable the blade to be positively fixed relative to the blade carrier/pressure piece combination.
Additional objects and advantages of the present invention will become apparent from a reading of the detailed description of the preferred embodiments which makes reference to the following set of drawings in which: